The invention relates to a magnetic transducer head for cooperating with (that is, transducing) a moving magnetic record medium (such as a magnetic tape) to play back signals along a record path extending in the direction of movement of the record medium.
To describe the improvements resulting from the present invention, it is first necessary to point out some deficiencies of conventional playback heads used for reproduction in an NAB tape cartridge recording and reproducing machine. The conventional head consists of a generally cubic metal casing with the face end wall constructed to resemble a hyperbola. The so-called hyperbolic nose at the face end wall makes excellent contact with the magnetic tape, providing superb high frequency response with minimal losses in the range of 1 to 15 kHz. By contrast, the low frequency response of the hyperbolic head leaves much to be desired when used with the NAB cartridge. Frequencies from 50 to 250 Hz are reproduced erratically, at different levels. There can easily be amplitude variations of .+-.2.5 decibels or more!
The low frequency response in cartridge machines is definitely inferior to that in open reel machines. After much research, the applicants were able to determine that the differences were due, in part, to the way that the tape wraps about the playback head in a cartridge machine as opposed to the type of wrap encountered in an open reel type player.
In an open reel tape recorder-reproducer, the tape path and its wrap about the face of the head is determined mechanically. Most professional open reel recorders do not have pressure pads, so the angles of approach to, and retreat from, the head face are determined totally by the positions of the tape guide rollers. On the other hand, in a cartridge machine, the tape is pressed against the head face by a compressible pressure pad. The actual wrap and the angles of approach and retreat are influenced by the strength and uniformity of the pressure pad itself which holds the moving tape against the head and conforms it to the approach and retreat angles of the head face. Since no two pressure pads are precisely alike, the results vary from one cartridge to another. This is aggravated by the high approach and retreat angles which are built into the head face of the conventional hyperbolic head. In this conventional head the tape runs along the surfaces of the pole piece portions fore and aft of the gap which surfaces are inclined at a steep angle of approximately 13.degree. from a base plane parallel to the general direction of movement of the tape. In a cartridge machine, the pressure pad within the cartridge presses the tape onto the inclined surfaces, but the 13.degree. angle is too great for the conventional pressure pad to conform the tape consistently to the approach and retreat surfaces. Because conformance is not 100% consistent, low frequency playback is degraded.